Make the apple filling: Place sliced apples in a medium/large bowl, then add the raisins and the lemon juice. Mix fruit to coat, then add the ¼ cup granulated sugar and mix to coat again. Set aside at room temperature.
Make the crumble topping: In another medium bowl, mix together the oats, flour, ¼ cup granulated sugar, brown sugar, and cinnamon.
Take the cold, cubed butter out of the fridge and use a pastry blender to cut the butter into the crumble topping. (You can use a fork, but a pastry blender works best.) Cut butter into the mixture until it makes coarse crumbs.
Pour the apple filling into the prepared 8x8 baking dish resting on the lined baking sheet. Smooth filling into an even layer, making sure some of the raisins are on the top.
Sprinkle handfuls of the crumble topping over the apples, making sure to cover every corner of the dish. Use all of the topping!
Bake the apple crumble on the lined baking sheet at 350F for 35-40 minutes, or until the filling is hot and bubbling around the edges and the crumble topping is golden and crunchy.
Remove apple crumble from oven and set on a wire cooling rack. Let cool for 10 minutes, then serve in bowls with ice cream or whipped cream.